First-time buyer US mortgage: what to put in the calculator
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By Editorial team
The same $380,000 US list price tells two different stories depending on how much cash you bring. With 5% down and a 7.0% conventional quote plus 0.62% PMI, month-one P&I plus MI runs about $2,775 and total modeled interest nears $503,627. Jump to 20% down at 6.75% with no PMI and the opening payment falls to about $1,972 while interest drops toward $405,826. That $97,801 difference is purely from the higher balance and PMI. Taxes, insurance, and HOA are not included in these figures; see the PITI guide below for a full monthly-cost picture.
The scenario modeled
Both tabs assume May 2026 funding, monthly billing, no taxes or insurance in the tool yet, and conventional pricing so you can stress-test equity versus rate versus PMI without mixing FHA MIP unless you open another tab yourself.
| Input | 5% down | 20% down |
|---|---|---|
| Cash to close (down) | $19,000 | $76,000 |
| Loan amount | $361,000 | $304,000 |
| Rate | 7.00% | 6.75% |
| PMI | 0.62% annual | None |
The findings
At 5% down, PMI cancels automatically once the loan reaches 80% of the original value, typically around year 11 on this balance and rate. Until then, the 5%-down borrower pays $803 more per month. That gap covers the PMI cost ($187/month) and the higher payment on a larger balance. Waiting an extra year to save for 20% down requires discipline. The math rewards it by roughly$97,801 over the loan's life.
| 5% down | 20% down | Difference | |
|---|---|---|---|
| Month 1 P&I + MI | $2,775 | $1,972 | $803/month lower with equity |
| Total interest (30 years) | $503,627 | $405,826 | $97,801 more at 5% down |
| Mortgage insurance | PMI until ~80% LTV (~yr 11) | None | $187/month until cancelled |
US context
Many first-time buyers focus on the down payment minimum and underestimate what comes next. The CFPB's homeownership resources note that property taxes, insurance, and escrow funding routinely add $500 or more per month on top of principal and interest, and are among the most common sources of budget surprise in the first year of ownership.
Source: Consumer Financial Protection Bureau (CFPB), "Buying a House," accessed April 2026. URL: https://www.consumerfinance.gov/owning-a-home/
When this checklist applies, and when it does not
Use it when you are translating pre-approval letters into forward-looking cash plans and want honest PMI math in the same window as rate quotes.
Defer it when you already know you are VA-eligible with no PMI, or when employer housing benefits change your effective down payment. Model those programs explicitly instead.
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Frequently asked questions
- What should a first-time buyer include in a mortgage calculator?
- Loan amount after down payment, rate quote, PMI or MIP if below 20% on conventional or FHA, term length, property taxes, homeowners insurance, HOA, and any credits you model as negative closing costs.
- How much more does a low down payment usually cost?
- Smaller equity means larger balances, mortgage insurance, and sometimes higher rates. In our modeled $380,000 home, 5% down at 7% with PMI carried about $98,000 more lifetime interest than 20% down at 6.75%.
- Do I need perfect credit to model FHA?
- You can model FHA assumptions in a separate tab, but pricing still depends on your score band and lender overlays. Use calculator outputs as conversation starters with a loan officer.
- Should I budget reserves beyond the down payment?
- Yes. Closing costs, moving expenses, and maintenance buffers matter more than squeezing the last $10 off a payment estimate.